This invention relates in general to subscription television systems (STV) and is particularly concerned with an addressable adapter for use in a cable television system (CATV).
In recent years the STV industry has expanded to an extent that today it furnishes television programming to millions of homes. In a CATV system, a cable serves as a direct link between a subscriber and the cable operator or, "head-end" of the system, that is, the source of the program signals. The cable is terminated, at the subscriber's installation, by a converter which converts the programs the subscriber is authorized to receive to the frequency of a standard VHF television signal (usually channel 3 or, in any event, a channel not already in use in the cable operator's service area), which VHF signal is then coupled to the subscriber's television receiver.
A typical early generation CATV converter, many of which are still in use today, has the subscriber's programming authorization preselected when the converter is initially set up in the subscriber's home. Such authorization preselection is necessitated by virtue of the fact that the cable frequently carries, in the form of video modulated RF carriers, all the programming available from the cable operator, thus each converter serves as a filter to limit the individual subscriber to the programs he is authorized to receive under his contract. Thereafter, should the subscriber wish to change the programming available to him, the cable operator must dispatch a service man to the subscriber's home to make a hands-on alteration of the subscriber's converter or to the trunk feeding that subscriber's cable. Since a programming change cannot be effected from the head-end, but entails a service call, this type of subscriber unit is designated a non-addressable converter.
Another shortcoming of a non-addressable converter is the inability of the cable operator, short of repossessing the converter or disconnecting the feeder cable at a trunk station, to prevent a delinquent subscriber from receiving programs.
Another segment of the STV industry transmits its signal over-the-air, but in a scrambled form so that non-subscribing viewers receive only a scrambled picture. This system also utilizes a converter for its subscribers which serves to unscramble the received signal so that it may be utilized on the subscriber's television receiver. Again, if the converter is non-addressable, the over-the-air system operator faces the same problems encountered by the cable operator. Accordingly, whenever reference is made herein to a "non-addressable CATV converter", it is to be understood that the term also contemplates a non-addressable converter designed to receive air-borne subscription television programs.
Recognizing the limitations of the basic system, a succeeding generation of CATV converters featured addressability, i.e., the ability to respond to command signals, in the form of encoded data, transmitted through the cable network (or, over-the-air) by the head-end. More particularly, in an addressable system each decoder is identified by a unique address so that the head-end can effectively interrogate that subscriber installation and then restrict or expand the programming available to the subscriber to that he is authorized to receive. Moreover, whenever the subscriber wishes to change his programming, he simply calls the head-end to add or delete the program(s) he desires. Since this new information can be instantly inserted into a computer, the subscriber's program authorization can be altered, effectively, at a moment's notice.
Additionally, addressability facilitates subscriber access to pay-per-view (PPV) programming, that is, special services not covered by the fee the subscriber pays for his day-to-day programming. Special services would contemplate championship boxing matches, premium movies, etc., which can be ordered by simply calling the head-end office.